Believe it or not ... -40°F.
The two scales have equal numerical values at this temperature.Its the same, -40 degrees Celsius = -40 degrees Fahrenheit.Start by taking the number in Celsius and...
- 40 °F = - 40 °C
The temperature of -40° is the same temperature on both scales.
Converting -40 °C to Fahrenheit is (9/5 x 40°) + 32° = -72° + 32° = -40°F.